The present invention relates to a process for preparing multi-block copolymers employing polar solvents. Multi-block copolymers and polymeric blends comprising the same are usefully employed in the preparation of solid articles such as moldings, films, sheets, and foamed objects by molding, extruding, or other processes, and are useful as components or ingredients in laminates, polymeric blends, and other end uses. The polymers comprise two or more differing regions or segments (blocks) differing in physical or chemical properties, such as crystallinity, tacticity, chain branching, and/or monomer insertion errors, thereby causing the polymer to possess unique physical properties. The resulting products are used in the manufacture of components for automobiles, such as profiles, bumpers and trim parts; packaging materials; electric cable insulation, adhesives, and other applications.
It is known in the art to prepare multi-block copolymers from one or more monomers by the use of chain shuttling agents under suitable polymerization techniques, especially continuous solution polymerization conditions at relatively high monomer conversions. Preferred processes employ two catalysts having differing comonomer incorporation properties and a chain shuttling agent such as organoaluminum and organozinc compounds. Examples include WO2005/904025, WO2005/904026, and WO2005/904027, as well as Science, 312, 714-719 (2006). Solvents for the foregoing processes generally include C4-10 hydrocarbons, especially alkanes such as hexane or mixtures of alkanes, as well as one or more of the monomers employed in the polymerization. In addition, toluene was employed in WO2005/904025 in designed experiments to identify suitable catalysts for chain shuttling polymerizations. In general, chain shuttling properties of aluminum compounds, especially trialkyl aluminum compounds, were found to be inferior to those of dialkyl zinc compounds under the conditions tested in these studies.
It would be desirable if there were provided an improved process for preparing multi-block copolymers, especially linear multi-block copolymers of ethylene and one or more C3-10 α-olefins, or propylene, 4-methyl-1-pentene, or another C4 or higher α-olefin(s), mixtures of two or more C3-10 α-olefins, and mixtures of ethylene, and/or propylene with a conjugated or non-conjugated C4-20 diene, by the use of a shuttling agent under chain shuttling polymerization conditions, characterized by improved efficiency and productivity. In addition, it would be desirable to provide such an improved process that is capable of preparing multi-block copolymers, especially linear multi-block copolymers, having improved (more narrow) molecular weight distribution employing organoaluminum chain shuttling agents, especially trialkylaluminum compounds. Finally, it would be desirable to provide an improved process for preparing any of the foregoing desirable polymer products in a highly productive, continuous solution polymerization process.